In many industries there exists a need to reduce large pieces of solid material to a particulate form. For instance, in managing wood and tree waste, it is desirable to grind stumps and wood scraps into wood chips. Wood chips are more easily and efficiently transported, stored, and used for various purposes. In other instances, it is desirable to reduce large pieces of waste material, such as plastic, for recycling or disposal. Comminuters of various size and operation are generally available for performing this function.
A particular style of comminuter presently available, sometimes referred to as a pan and disk refiner, includes a comminuting chamber defined by a rotating sidewall and a bottom disposed across an end of the sidewall. U.S. Pat. No. 5,379,951, commonly assigned to the assignee of the present invention, discloses a comminuter of this style and is expressly incorporated herein by reference. Inside the comminuting chamber, a toothed disk is rotatably mounted at the bottom in a plane spaced above the bottom. Operators of the comminuter introduce material to be comminuted into the chamber where it engages the toothed disk and is reduced to particulate form.
The comminuter operates by rotating both the chamber sidewall and the toothed disk, usually in opposite directions. The rotation of the sidewall imparts rotational motion to the material placed in the chamber. As the material in the chamber rotates with the chamber sidewall, the material comes into contact with the rotating toothed disk. The teeth on the disk impact the material and thereby rip and tear the material into successively smaller pieces. The comminuting chamber typically further has a screened exit through which the material, once comminuted to a particular size, may pass out of the chamber.
During the comminuting process, material sometimes falls flat on the bottom of the chamber and avoids further contact with the rotating toothed disk. If a screened exit is also located on the chamber bottom and the material is not small enough to pass through the screen, the material may clog up the screen and prevent material that is comminuted to a sufficiently small size from exiting the comminuting chamber. Operation either continues at a lower production level, or the operator of the comminuter may need to turn the comminuter off and reorient the material in the comminuting chamber so that all of the material may properly engage the disk and to clear the screen.
Another disadvantage with present comminuters is jamming of the comminuting chamber. On occasion, a large chunk of material may lodge between the toothed disk and the sidewall, causing the comminuting chamber to jam. A comminuting chamber is particularly susceptible to violent jamming when the toothed disk and the sidewall are rotating in the same direction. Usually, if the comminuter operator is vigilant, such a jam may be remedied by reversing the rotation of the disk. However, in some instances, it may be necessary to turn the comminuter off and manually dislodge the jammed material.
Another problem inherent with present comminuters is the collection of material adhering to the chamber sidewall. Tree stumps introduced into a comminuting chamber may carry soil into the chamber which may collect on the chamber sidewall. Material that is wet also tends to collect on the chamber sidewall. Debris that adheres to the chamber sidewall increases the weight of the sidewall, thereby demanding increased power from the comminuter to continue sidewall rotation. The debris may also hold material to be comminuted above the toothed disc and discharge screen. The efficiency of the comminuter is accordingly diminished.
A partial solution to these problems was provided in a prior comminuter developed by the present inventor and sold by Universal Refiner Corp. A comminuter of the type disclosed in U.S. Pat. No. 5,379,951 was provided with a rotary, star-shaped screen scrubber. This conventional scrubber has a center hub journaled to the stationary bottom wall of the comminuter chamber, adjacent the annular screened exit. The scrubber included a plurality of radial arms that projected only partially, i.e., about a third of the way, across the width of the screen to agitate comminuted material passing the scrubber. However, the scrubber left a substantial portion of the screen unscrubbed, reducing effectiveness.
The present invention is designed to provide solutions to these problems.